1. Field of the Invention
This invention relates to a die for manufacturing a laminated core constituting a rotor or a stator for an electric motor or a generator and more particularly a die for manufacturing a laminated core in which rotary stacking and skewing can be simultaneously carried out when thin core plates punched to a predetermined shape are stacked.
2. Description of the Prior Art
A rotor of an electric motor or a generator is constructed such that sheet-like thin plates, forming a laminate core are punched to a predetermined shape and several thin core plates are stacked together.
Although a wide, thin iron plate from which the sheet-like thin iron plates are cut and formed is made by rolling the wide, thin iron plate between rollers, the thickness of the wide, thin iron plate is not uniform over the entire width of the plate due to the flexibility of the pressing rollers. Accordingly, when the thin core plates (a) punched from the sheet-like thin iron plate are piled up to constitute a laminated core L, as shown in FIG. 10, a height of the laminated core L in its circumferential direction is not uniform but shows a deformation under the influence of a difference delta in plate thicknesses.
In order to eliminate the influence of the difference of the plate thicknesses, as shown in FIG. 11 in the prior art, the thin core plates (a) are rotated in sequence by 90.degree. or 180.degree. and stacked in a rotary stacking process.
In order to improve an electrical characteristic of the laminated core, the thin plates constituting the laminated core L are displaced by a minute angle and stacked together as a whole, as shown in FIG. 3, and slots 11 are formed in a slant manner. This skewing is further carried out simultaneously with the rotary stacking process.
As described above, a die for manufacturing a laminated core capable of simultaneously performing rotary stacking and skewing as well as punching the iron, thin core plates, are shown in prior art patents such as U.S. Pat. Nos. 4,619,028; 4,738,020; and 4,704,184 (corresponding to Jap.Pat.Laid-Open No.Sho 60-170,534) or the like. As to a Japanese patent, the device disclosed in Jap.U.M.Publn.No.Sho 63-44178 is already known.
In case of the die devices disclosed in U.S. Pat. Nos. 4,619,028 and 4,738,020, a rotational force of the servo-motor is applied to the rotary die arranged in a lower die punching and stacking station, and this die is rotated by an angle required for performing the rotary stacking and skewing operations. However, such a system as described above has a problem that sufficient accuracy in an indexing angle with the servo motor may not be attained and a laminated core of high performance may not be provided. Under a condition in which the thin iron plates are punched and stacked at under a high speed, there is a problem that a following characteristic in operation of the servo mechanism may not be sufficiently attained and thus efficient manufacturing of the laminated cores may not be achieved. In addition, if the outer shape of the laminated cores to be manufactured is large, there may be a problem of availability of a suitable servo motor.
In the die disclosed in U.S. Pat. No. 4,704,184, it is disclosed that the rotary die is applied with a rotation of a desired angle required for performing rotary stacking as well as a skewing operation under a combination of a transmission device composed of gears and an indexing device. This die has a problem that the die is large in size as the transmission device includes a combination of gears and at the same time replacement of the gears of the transmission device is required when the rotational angle is to be varied and further it has an another problem that it takes much time to prepare for operation. In addition, in case of the combination of the gears, since a transmission ratio may not be adjusted in a stepless manner, it sometimes happens that the required rotational angle may not be attained.